Clathrin-Coated Vesicles and Vesicle Fusion
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Clathrin-Coated Vesicles and Vesicle Fusion

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Questions and Answers

What type of proteins regulate the formation of clathrin-coated vesicles?

  • Transmembrane proteins
  • Collagen proteins
  • Phospholipid proteins
  • GTP-binding proteins (correct)

    • Clathrin interacts directly with the cargo proteins in vesicle transport.

    False

    What is the diameter range of clathrin shells?

    700–800 Å

    The _____ proteins direct vesicles to the correct membrane.

    <p>Rab</p> Signup and view all the answers

    Match the following terms with their descriptions:

    <p>Triskelion = Structure formed by heavy chains of clathrin Adaptor proteins = Mediators for clathrin and cargo assembly SNARE proteins = Proteins that facilitate vesicle fusion Tethering factors = Proteins that help bind vesicles to target membranes</p> Signup and view all the answers

    What is the primary function of SNARE proteins?

    <p>Mediate vesicle fusion</p> Signup and view all the answers

    Light chains are involved in the polymerization of heavy chains in clathrin.

    <p>True</p> Signup and view all the answers

    What shape do clathrin vesicles typically take due to natural curvature?

    <p>spherical</p> Signup and view all the answers

    What is the role of the trans Golgi network in protein packaging?

    <p>Sorting and packaging into transport vesicles</p> Signup and view all the answers

    Regulated secretory pathways include the release of ions from muscle cells.

    <p>False</p> Signup and view all the answers

    What are sec mutants in yeast?

    <p>Yeast mutants defective at various stages of protein secretion.</p> Signup and view all the answers

    The addition of carbohydrates to ceramide yields a variety of different ___.

    <p>glycolipids</p> Signup and view all the answers

    Match the category of vesicular transport with its description:

    <p>Direct transport = Transport directly to the plasma membrane Recycling endosomes = Transport involving the recycling of membrane components Regulated secretion = Transport requiring signals to release substances Secretory granules = Storage of proteins until needed for secretion</p> Signup and view all the answers

    Which molecule is synthesized from ceramide in the Golgi apparatus?

    <p>Sphingomyelin</p> Signup and view all the answers

    Vesicles must recognize and fuse with any available membrane.

    <p>False</p> Signup and view all the answers

    What type of transport do COPII-coated vesicles facilitate?

    <p>Transport from the ER to Golgi apparatus</p> Signup and view all the answers

    Identify one experimental approach used to study vesicular transport.

    <p>Isolation of yeast mutants defective in protein transport.</p> Signup and view all the answers

    Synaptic transmission in neurons involves the release of chemical neurotransmitters that are stored in synaptic vesicles.

    <p>True</p> Signup and view all the answers

    What is the function of cDNA in studying vesicular transport?

    <p>to encode secretory proteins tagged with fluorescent markers</p> Signup and view all the answers

    Synaptic vesicles are purified from ______ tissue for the study of protein isolation.

    <p>brain</p> Signup and view all the answers

    What is the purpose of using GFP fusion proteins in research?

    <p>To visualize transport vesicles carrying specific proteins</p> Signup and view all the answers

    Match the following vesicle coat proteins with their respective transport functions:

    <p>COPII = Anterograde transport from ER to Golgi COPI = Retrograde transport from Golgi to ER Clathrin = Transport of vesicles in endocytosis</p> Signup and view all the answers

    Immunostaining is a technique that allows visualization of ______ protein location in fixed cells.

    <p>intercellular</p> Signup and view all the answers

    The mechanism of vesicular transport does not involve the removal of coat proteins before the vesicle reaches its target.

    <p>False</p> Signup and view all the answers

    Study Notes

    Clathrin-Coated Vesicles

    • Clathrin-coated vesicles transport molecules between the trans Golgi network (TGN), endosomes, lysosomes, and the plasma membrane.
    • Vesicle formation is regulated by small GTP-binding proteins (ARF1 and Sar1) which are related to Ras and Ran GTPases.
    • GTP-binding proteins recruit adaptor proteins that interact with cargo proteins and coat proteins.
    • Clathrin has two polypeptide chains: heavy chain (190 kDa) and light chain (14 kDa).
    • Heavy chains associate at their C-termini to form a triskelion structure.
    • Light chains modulate heavy chain polymerization.
    • Clathrin lattices define the shape of vesicles.
    • Clathrin coated vesicles are typically 700–800 Å in diameter and contain 35–40 triskelions.
    • Clathrin does not interact directly with cargo. Adaptor molecules recruit clathrin and cargo.

    Vesicle Fusion

    • Small GTP-binding proteins called Rab proteins direct vesicles to the correct membrane.
    • Rab proteins interact with the vesicle coat and reside on the cytoplasmic surface of the vesicle.
    • Tethering factors and Rab proteins mediate fusion between transport vesicles and target membranes
    • Tethering factors can also bind to coat proteins and stimulate formation of complexes between SNAREs.

    SNARE Proteins

    • SNARE proteins mediate vesicle fusion.
    • Synaptic transmission in neurons is a specialized form of regulated secretion.
    • Neurotransmitters are stored in synaptic vesicles.
    • Stimulation of the neuron triggers fusion of synaptic vesicles with the plasma membrane.

    Visualizing Vesicular Transport

    • Fluorescent microscopy allows real-time observation of vesicular transport.
    • Cells can be transfected with cDNA encoding secretory proteins tagged with green fluorescent protein (GFP).
    • GFP fusion proteins allow transport vesicles carrying specific proteins to be visualized by fluorescence.
    • GFP might interfere with protein function and localization.
    • Alternatively, fluorescent antibodies can be used to visualize intercellular protein location via immunostaining.

    Transport Vesicle Coats

    • Transport vesicles from the ER are coated with cytosolic coat proteins.
    • Coats are removed before the vesicle reaches its target.
    • Three families of vesicle coat proteins:
      • COPII-coated vesicles transport from the ER to the ERGIC and Golgi.
      • COPI-coated vesicles transport from the ERGIC or Golgi back to earlier compartments.
      • Clathrin-coated vesicles transport between the TGN, endosomes, lysosomes, and the plasma membrane.

    The Golgi Apparatus

    • Glycolipids and sphingomyelin are synthesized from ceramide in the Golgi.
    • Ceramides are composed of sphingosine and a fatty acid tail.
    • Sphingomyelin is synthesized by transferring a phosphorylcholine group from phosphatidylcholine to ceramide.
    • Glycolipids are formed by the addition of carbohydrates to ceramide.

    Protein Sorting and Export in Golgi

    • In the TGN, molecules are sorted and packaged into transport vesicles.
    • Proteins that need to stay in the Golgi contain signals that prevent packaging and transport.
    • Transport from the Golgi to the cell surface can occur via three routes:
      • Direct transport to the plasma membrane
      • Recycling endosomes
      • Regulated secretory pathways
    • Regulated pathways include release of hormones and neurotransmitters.
    • These proteins aggregate in the TGN and are packaged in secretory granules.
    • The granules store their contents until signals direct their fusion with the plasma membrane.

    Membrane Domains

    • Polarized cells of epithelial tissue have apical and basolateral domains with specific proteins.
    • Proteins leaving the TGN must be selectively packaged and transported to the correct domain.

    Studying Vesicular Transport

    • Understanding the mechanisms that control vesicular transport is a major area of research.
    • Three approaches have been used for studying vesicular transport:
      • Isolation of yeast mutants defective in protein transport and sorting
      • Reconstitution of vesicular transport in cell-free systems
      • Biochemical analysis of synaptic vesicles

    Yeast Mutants

    • Yeast mutants can be defective at various stages of protein secretion (sec mutants), or are unable to transport proteins to the vacuole, or retain resident ER proteins.

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    Lecture 10 Cargo Packaging and Vesicular Fusion PDF

    Description

    Explore the intricate processes of clathrin-coated vesicles and vesicle fusion in cellular transport. This quiz covers the roles of GTP-binding proteins, adaptor proteins, and the structure of clathrin in the formation and function of vesicles. Test your understanding of key concepts in cellular biology related to vesicular transport.

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